Process for preparing water soluble polyaluminosilicates

ABSTRACT

An improved method for the production of water soluble polyaluminosilicate microgels, formed by the reaction of solutions of alkali metal silicates with solutions of acids containing dissolved aluminum compounds, is provided.

FIELD OF THE INVENTION

This invention relates to water soluble polyaluminosilicate microgelsand specifically to an improved process for making them.

BACKGROUND OF THE INVENTION

The formation of water soluble polyaluminosilicate microgels and theiruse in papermaking is known. U.S. Pat. No. 5,176,891 discloses a processfor their production involving the initial formation of a polysilicicacid microgel followed by reaction of the polysilicic acid microgel withan aluminate to form the polyaluminosilicate. The use of thepolyaluminosilicate microgels as improved retention and drainage agentsin papermaking is also disclosed. U.S. Pat. No. 5,127,994 discloses aprocess for the production of paper by forming and dewatering acellulosic fiber suspension in the presence of three compounds: analuminum salt, a cationic polymeric retention agent and polysilicicacid.

The polyaluminosilicate microgel process disclosed in U.S. Pat. No.5,176,891 comprises three steps, namely, (1) the acidification of awater solution of an alkali metal silicate to form polysilicic acidmicrogel, (2) addition of a water soluble aluminate to the polysilicicacid microgel to form the polyaluminosilicate and (3) dilution tostabilize the product against gelation. There is a necessary agingperiod involved following the acidification step during which thesilicic acid first formed polymerizes to linear polysilicic acid andthen to the microgel structure which is critical to the performance ofthe polyaluminosilicate products. The products are described as having asurface area of greater than 1000 square meters per gram, a surfaceacidity of greater than about 0.6 milliequivalents per gram and analumina/silica mole ratio of greater than 1:100, preferably between 1:25and 1:4.

The method of the present invention is an improvement over the processdescribed in the '891 patent in that it combines the acidification andalumination steps. An unexpected and important benefit resulting is thatthe aging period required for microgel formation to occur issignificantly reduced. The polyparticulate polyaluminosilicate productsproduced by the process of this invention have good activity asretention and drainage agent in paper making immediately on formation(no aging period) and they reach their optimum performance insignificantly less time than those prepared by previous methods. Agingperiods required for product formation are avoided or minimized wheneverpossible in paper making since they require additional or oversizedequipment and are known to give rise to problems such as products ofuneven quality. Any reduction in the aging period is thus an improvementin the process of paper making and in product quality.

SUMMARY OF THE INVENTION

The process of this invention for producing water solublepolyparticulate polyaluminosilicate microgels having mole ratios ofalumina:silica of between 1:10 and 1:1500 comprises the steps of

(a) acidifying an aqueous solution of an alkali metal silicatecontaining 0.1-6% by weight of SiO₂ to a pH of 2-10.5 by using anaqueous acidic solution containing an aluminum salt; and

(b) diluting the product of step (a) with water prior to gelation to aSiO₂ content of ≦2% by weight.

DETAILED DESCRIPTION OF THE INVENTION

An important aspect of the process of this invention is the addition ofa water soluble aluminum salt to an acid used for the acidification ofan alkali metal silicate solution. This way, hydrated aluminum hydroxideis produced at the same time as silicic acid and thus, during thepolymerization of silicic acid to polysilicic acid and formation of apolyparticulate microgel, aluminum hydroxide is incorporated directlyinto the polymer with the attendant formation of polyaluminosilicate.This process can produce useful polyaluminosilicates (PAS) over a widerange of compositions having alumina/silica mole ratios ranging fromapproximately 1:1500 to 1:10 but generally about 1:1000 or less,preferably 1:750 to 1:25 and most preferably 1:500 to 1:50. Because ofthe low alumina/silica ratio, the total surface acidity of thepolyaluminosilicates does not differ significantly from that ofnon-aluminated polysilicate microgels. At the same time an anioniccharge is maintained into lower pH ranges than is observed withnon-aluminated polysilicic acid.

The process of this invention can be carried out as a two-step processcomprising

(a) acidifying an aqueous solution of an alkali metal silicatecontaining 0.1-6% by weight of SiO₂ to a pH of 2-10.5 by using anaqueous acidic solution containing an aluminum salt; and

(b) diluting the product of step (a) with water prior to gelation to aSiO₂ content of ≦2% by weight.

Optionally, after the acidification step, an aging step can be employedto improve product performance further. Such an aging period is notrequired and is somewhat counter to the benefit gained from the processof this invention, a reduction in the time required for thepolyaluminosilicate products to reach maximum activity. The agingperiod, if employed, can be any period of time up to that required forthe gelation of the reaction mix. This can vary from seconds to hoursdepending on the particular reaction conditions employed.

Any water soluble silicate salt can be used in the present process,alkali metal silicates such as sodium silicate being preferred. As anexample, sodium silicate, Na₂ O:3.2SiO₂, by weight, can be used.

Any acid with a pKa less than about 5 can be used. Inorganic mineralacids are preferred over organic acids; sulfuric acid is the mostpreferred.

Any aluminum salt can be used which is soluble in the acid used.Suitable choices are aluminum sulfate, chloride, nitrate and acetate.Basic salts such as sodium aluminate and chlorohydrol, Al(OH)₂ Cl, canalso be used. If alkali metal aluminates are used, they can be firstconverted to an aluminum metal salt by reaction with the acid.

To carry out the process of the invention, a dilute aqueous solution ofan alkali metal silicate, containing from about 0.1-6 wt % SiO₂,preferably about 1-5 wt % SiO₂ and most preferably 2-4 wt %, is rapidlymixed with a dilute aqueous solution of an acid containing a dissolvedaluminum salt so as to produce a solution within a pH range of about2-10.5. A more preferred pH range is from 7-10.5 with the most preferredrange being pH 8-10. Suitable acid concentrations range from 1-50 wt %although both lower and higher concentrations can be used providedadequate mixing is employed. Generally a concentration of about 20 wt %acid is preferred. The amount of aluminum salt dissolved in the acidsolution can vary from about 0.1 wt % up to the limit of solubility ofthe salt in the acid.

The mole ratio of Al₂ O₃ /SiO₂ in the polyaluminosilicate microgelsproduced by the process of this invention can vary widely from about1:1500 to 1:10 depending upon the concentration of the acid used, theamount of aluminum salt dissolved in the acid and the pH of theresulting partially neutralized silicate solution. Acidification intolower pH ranges requires the use of more acid and can result in theproduction of polyaluminosilicates containing higher alumina/silica moleratios. Solubility data of an Al₂ (SO₄)₃ --H₂ SO₄ --H₂ O system (Linke,"Solubility of Inorganic Compounds", 4th Ed. 1958, Vol. 1) provide abasis for calculating the maximum Al₂ O₃ /SiO₂ ratios obtainable inpolyaluminosilicates (when using Na₂ O:3.2SiO₂ as the silicate) usingsulfuric acid solutions containing from 10-50 wt % acid, saturated withaluminum sulfate, for the acidification of a silicate solution to pH 9.(At this pH, approximately 85% of the alkalinity of Na₂ O:3.2SiO₂ isneutralized.)

    ______________________________________                                        H.sub.2 SO.sub.4                                                                         Al.sub.2 (SO.sub.4).sub.3                                                               Polyaluminosilicate                                      Wt %       Wt %      Al.sub.2 O.sub.3 /SiO.sub.2 mole ratio                   ______________________________________                                        10         19.6      1/22                                                     20         13.3      1/32                                                     30         8.1       1/61                                                     40         4.3       1/138                                                    50         2.5       1/283                                                    ______________________________________                                    

It has been found that the process of preparing PAS microgels canpreferably be carried out using an acid solution containing about 20 wt% sulfuric acid and from 1-6 wt % of dissolved aluminum sulfate. Usingsuch acid solutions over the preferred pH range of 8-10 (representingapproximately 95-60 wt % neutralization of Na_(20:3).2 SiO₂),polyaluminosilicate microgels with Al₂ O₃ /SiO₂ mole ratios of fromabout 1:35 to 1:400 can be obtained. Within the preferred concentrationand plI ranges, the polyaluminosilicate solutions are clear and, afterdilution to about 0.5 wt % SiO₂, retain their activity in flocculationprocesses for about 24 hours.

The polyaluminosilicates produced by the process of this invention canbe utilized in a wide variety of flocculation processes and act asretention and drainage agents in paper making (used in the amount of0.01-1% by weight, based on the dry weight of the paper furnish). Theyare employed in combination with cationic polymers such as cationicstarch, cationic polyacrylamide and cationic guar. These are describedin U.S. Pat. No. 4,927,498 and U.S. Pat. No. 5,176,891. Such (watersoluble) cationic polymers are present to the extent of at least about0.001 weight % based on the dry weight of the furnish. Anionic polymerssuch as anionic polyacrylamide can also be used in conjunction with thepolyaluminosilicate microgels and cationic polymers with beneficialresults. Depending on the papermaking conditions, various otherchemicals can also be employed in conjunction with thepolyaluminosilicate microgels and high molecular weight cationicpolymers. In systems containing large amounts of anionic trash, forexample, low molecular weight, high charge-density cationic polymerssuch as polyethyleneimine, polydiallyldimethylammonium chloride andamine-epichlorohydrin condensation products can be added to achieve acharge balance within the system more effectively and obtain improvedresults. Additional quantities of aluminum salts beyond those containedin the acidic solution, such as alum and sodium aluminate, can also beadded for improved results in certain circumstances. These can be addedto the papermaking furnish either by premixing with thepolyaluminosilicate microgels of this invention or by separate addition.

EXAMPLE 1

Preparation of PAS Microgel

300 g of a water solution of sodium silicate (Na₂ O:3.2SiO₂) containing4 wt % SiO₂ was acidified to pH 10 using 20 wt % sulfuric acidcontaining 1.5 wt % of aluminum sulfate [Al₂ (SO₄)₃ ]. The acid wasadded from a burette into the silicate solution stirred with a magneticstirrer. The polyaluminosilicate product had an Al₂ O₃ /SiO₂ mole ratioof 1:25 1 as calculated from the amount of aluminum sulfate-containingacid solution used. Immediately after completion of the addition, asample was removed and diluted to 0.5 wt % of silica. Further sampleswere taken and diluted after the polyaluminosilicate microgel had agedfor 2, 7, 36, 96 and 156 minutes, respectively, and the diluted samplesevaluated for drainage performance.

For comparative purposes, a polyaluminosilicate of equivalentcomposition was prepared according to the method described in U.S. Pat.No. 5,176,891, as follows: 300 g of the same 4 wt % SiO₂ -containingsodium silicate solution was acidified to pH 10 using 20 wt % sulfuricacid only. The polysilicate microgel formed was sampled (and diluted 0.5wt %) on the same time schedule as above. Prior to evaluation it wasconverted to a polyaluminosilicate having an Al₂ O₃ /SiO₂ mole ratio of1:25 1 by the addition of sufficient amount of sodium aluminate solutionto obtain the desired ratio.

All samples were evaluated for drainage performance by Canadian StandardFreeness tests using an alkaline furnish of 0.4 wt % consistencycontaining 80% bleached Kraft pulp (50% hardwood/50% softwood) and 20%precipitated calcium carbonate. pH was 8.06. For drainage measurements,a standard addition of 20 lb/t (dry furnish weight basis) of cationicpotato starch (DS=0.03) followed by 2 lb/t (SiO₂ basis) of the variouspolyaluminosilicate samples were made to 11 of furnish contained in aBritt jar stirred with a mechanical stirrer at 1000 rpm (in order toflocculate the furnish prior to the drainage test). The flocculatedfurnish was then transferred to a cup of a Canadian Standard Freenesstester and the drainage measurements were made. Table 1 gives theresults obtained.

                  TABLE 1                                                         ______________________________________                                        PAS Microgel Age                                                                              Freeness (ml)                                                 (minutes)       This Invention                                                                            '891 patent                                       ______________________________________                                         0              605         520                                                2              650         585                                                7              655         605                                               36              670         640                                               96              660         650                                               156             650         630                                               ______________________________________                                    

The results demonstrate that the polyaluminosilicate produced by theprocess of this invention unexpectedly achieved approximately 90% of itsmaximum activity immediately after preparation compared to approximatelyonly 80% of maximum activity for the prior art polyaluminosilicate. Alsoand again unexpectedly, an improved performance was maintainedthroughout the aging period. The polyaluminosilicate of this inventionreached its maximum activity in a shorter period of time than thatprepared using the prior art method (36 minutes versus 96 minutes) andattained a higher freeness value (670 versus 650 ml).

It is believed that such improved performance, especially the reducedtime required to reach maximum activity, although not a prioripredictable, may be due to the catalytic effect of the presence of thealuminum salt throughout the formation of the particles in the 1-2 nmdiameter range and of the microgel structure. The aluminum ions areexpected to be present both within as well as on the surface of theparticles, i,e,, intra- and inter-particle.

EXAMPLE 2

Preparation of PAS Microgels

Four separate polyaluminosilicate samples having differing Al₂ O₃ /SiO₂mole ratios were prepared as follows:

Four 300-g aliquots of a 4 wt % SiO₂ solution (as Na₂ O:3.2SiO₂) wereacidified to pH 10 with 20 wt % sulfuric acid containing varying amountsof dissolved aluminum sulfate. By varying the amount of dissolvedaluminum sulfate from 1-6 wt %, products with alumina/silica mole ratiosbetween 1:78 and 1:248 were obtained as calculated from the amount ofacid used to reach pH 10 and the known amount of aluminum sulfatedissolved in the acid. After preparation, each product was aged for twominutes, then diluted to 1 wt % SiO₂ content and examined for anioniccharge by means of an Electrokinetic Sonic Amplitude device (MatecInstruments Inc., Hopkinton, Mass. 01748). Thereafter, thepolyaluminosilicate was titrated with 1N hydrochloric acid to the pH ofzero charge and thus the anionic pH range determined.

A control polysilicic acid microgel (without any aluminum) was alsoprepared using 20 wt % sulfuric acid for the acidification and examinedsimilarly. The results are given in Table 2; wherein the zero charge pHis that pH where the particle surface is electrically uncharged. A lowerzero charge pH, achieved by the PAS microgels of this invention, meansthat such particles carry an anionic charge in a broader pH range and,therefore, can be utilized as retention and drainage aids under the morewidely varied conditions of both acid and alkaline paper making.

                  TABLE 2                                                         ______________________________________                                        Zero charge pH of polyaluminosilicates                                        Al.sub.2 O.sub.3 /SiO.sub.2                                                                   Zero Charge                                                   mole ratio      pH                                                            ______________________________________                                        0 (Control, PSA)                                                                              6.45                                                          1:248           5.54                                                          1:190           4.92                                                          1:129           4.25                                                          1:76            3.82                                                          ______________________________________                                    

EXAMPLE 3

Preparation of Various PAS Microgels--A Comparison

In this test series, several different silicate microgels were producedto compare various prior art processes to the process of producing PASmicrogels of this invention to determine the aging time required toreach maximum activity and to measure ultimate performance. Included inthis test were several controls.

All of the products were evaluated for drainage performance by CanadianStandard Freeness tests using an alkaline furnish of 0.3 wt %consistency at pH 7.5. The furnish contained 70% bleached Kraft pulp(80% hardwood/20% softwood) and 30% precipitated calcium carbonate. Alladditions to the furnish were made in a Britt jar stirred with amechanical stirrer at 750 rpm in order to flocculate the furnish priorto the drainage tests. Product performance was tested by adding to apaper furnish 20 lb/t (dry furnish weight basis) of cationic potatostarch (DS=0.03), alum [Al₂ (SO₄)₃ •18 H₂ O] solution, when utilized, atthe ratios indicated below and 2 lb/t (SiO₂ basis) of the product beingtested.

Additions of various ingredients to a Britt jar were made 15 secondsapart. Mixing was stopped 15 seconds after the addition of the producttest samples. The flocculated furnish was then transferred to a CanadianStandard Freeness tester and drainage measurements were made. Watercollected from the freeness tester was measured for turbidity as anindication of the effectiveness of the samples to aid retention of thepulp fiber and filler.

Test Sample A was produced by deionizing a 292-g water solution ofsodium silicate (Na₂ O:3.2 SiO₂) containing 5 wt % SiO₂ with 200 g ofDowex® 50W-8X H ⁺ Form resin. The resin was added to the well stirredwater solution batch-wise. The resin was removed by filtration 3 minutesafter the mixture reached pH=3.0. Aliquots were removed at the timesshown in Table 3; zero time being when the mixture reached pH=3.0. Eachaliquot was then immediately diluted to 0.125 wt % SiO₂ to preventfurther microgel formation and was added to a paper furnish as describedabove (test A1).

Test Sample B was produced by deionizing a 300.5-g water solution ofsodium silicate containing 2 wt % SiO₂ with 100 g of Dowex® 50W-8XH⁺Form resin. The resin was added to the well stirred water solutionbatch-wise. The resin was removed by filtration 3 minutes after themixture reached pH=3.0. Aliquots were removed at the times shown inTable 3; zero time being when the mixture reached pH=3.0. Each aliquotwas then immediately diluted to 0.125 wt % SiO₂ for use in tests B1 andB2. (In test B1 no alumina was present in the furnish while in test B2,sufficient alum was added to the furnish to provide a 1:100 Al₂ O₃ /SiO₂molar ratio.) An identical set of aliquots was removed as above andimmediately diluted to 0.5 wt % SiO₂. Sufficient amounts of sodiumaluminate solution (0.5 wt % Al₂ O₃) were added to these dilutedaliquots to give a 1:100 Al₂ O₃ /SiO₂ molar ratio. These aliquots wereused in test B3.

Test Sample C was prepared by adding 12.5 ml of 5N sulfuric acid to a291-g water solution of sodium silicate containing 2 wt % SiO₂ to obtaina pH of 3.1. Aliquots were removed and diluted to 0.125 wt % SiO₂ foruse in tests C1 and C2. (In test C1 no alumina was present in thefurnish while in test C2, sufficient alum was added to the furnish toprovide a 1:100 Al₂ O₃ /SiO₂ molar ratio.) An identical set of aliquotswas removed as above and immediately diluted to 0.5 wt % SiO₂.Sufficient amounts of sodium aluminate solution (0.5 wt % Al₂ O₃) wereadded to these diluted aliquots to give a 1:100 Al₂ O₃ /SiO₂ molarration and used in test C3.

Test Sample D was prepared by adding 10.0 ml of 5N sulfuric acid to a291-g water solution of sodium silicate containing 2 wt % SiO₂ to afforda pH value of 9.0. Aliquots were removed and diluted to 0.125 wt % SiO₂for use in tests D1. In test D1 no alumina was present in the furnish.

Test Sample E was prepared utilizing the process of this invention byadding 10.0 ml of 5N sulfuric acid in which 0.68 g of aluminum sulfate[Al₂ (SO₄)₃ •18 H₂ O] had been dissolved to a 291-g water solution ofsodium silicate containing 2 wt % SiO₂ to afford a pH of 8.0. Theresulting polyaluminosilicate had a calculated Al₂ O₃ /SiO₂ molar ratioof 1:100. Aliquots were removed and diluted to 0.125 wt % SiO₂ for usein Test E1 as described above.

Test Sample F was prepared utilizing the process of this invention byadding 10.0 ml of 5N sulfuric acid in which 0.055 g of aluminum sulfate[Al₂ (SO₄)₃ •18 H₂ O] had been dissolved to a 291-g water solution ofsodium silicate containing 2 wt % SiO₂ to afford a pH of 8.9. Theresulting polyaluminosilicate had a calculated Al₂ O₃ /SiO₂ molar ratioof 1:1275. Aliquots were removed and diluted to 0.125 wt % SiO₂ for usein Test F1. The furnish contained sufficient alum to provide a final Al₂O₃ /SiO₂ molar ratio of 1:100.

Tests G through J were carried out as controls. Test G used onlycationic potato starch as a drainage aid. Test H used cationic potatostarch and alum (Al₂ O₃ at dosage equivalent to test J). Test I usedcationic potato starch and commercial BMA-0 colloidal silica (5nanometer spherical particles). Test J used cationic potato starch,alum, and BMA-0 colloidal silica (Al₂ O₃ /SiO₂ ratio=1/100). All dataare shown in Table 3.

As can be seen from Table 3, PAS microgels prepared using the process ofthis invention (Tests E1 and F1) reached their maximum activity faster,as measured by freeness and turbidity determinations in a paper makingprocess than those prepared by methods disclosed in the prior art, Viz.,U.S. Pat. No. 5,176,994 (Tests B2 and C2); U.S. Pat. No. 5,176,891 andU.S. Pat. No. 4,927,498 (Tests B3 and C3); and U.S. Pat. No. 4,954,220(Tests A1, B1, C1 and D1). PAS microgels of this invention also showedsuperior results in paper making after a 5-min. aging period than thoseof the prior art. These microgels gelled prior to the 1-hr.measurements; can be diluted from 2% to 0.5% (SiO₂) to prevent gelation.The PAS microgels of this invention also were shown to be superior tothe controls (Tests G, H, I and J).

                  TABLE 3                                                         ______________________________________                                        FREENESS/TURBIDITY vs. AGE TIME                                                                                       24                                    TEST  1 MIN    5 MIN    1 HOUR  4 HOUR  HOUR                                  ______________________________________                                        A1    470/83   470/78   500/65  500/61  585/28                                B1    410/111  435/111  4351103 425/110 475/61                                B2    440/96   440/102  450/98  475/77  540/39                                B3    480/67   495/63   475/83  480/69  520/49                                C1    400/125  420/121  425/116 405/126 420/109                               C2    410/122  430/119  420/123 420/127 420/102                               C3    420/116  420/122  415/119 415/108 460/66                                D1    490/62   570/39   630/21  615/21  555/29                                E1    510/58   620/26   GELLED  ˜20 MIN                                 F1    580/28   650/21   GELLED  ˜75 MIN                                 ______________________________________                                        TEST  FREENESS/TURBIDITY                                                      ______________________________________                                        G     380/154                                                                 H     390/131                                                                 I     450/72                                                                  J     510/49                                                                  ______________________________________                                    

EXAMPLE 4

In this test series, two different silicate microgels were prepared toshow that the incorporation of aluminum into the microgel structure asdescribed herein affords polyaluminosilicate microgels which aresuperior retention and drainage agents in paper furnishes below pH 7when compared to polysilicate microgels without aluminum.

These products were evaluated for drainage performance by CanadianStandard Freeness tests using a furnish of 0.3 wt % consistency. Thefurnish contained 80% bleached Kraft pulp (80% hardwood/20% softwood)and 20% Kaolin clay. The pH of the furnish was adjusted prior to eachtest as shown in Table 4. All additions to the furnish were made in aBritt jar stirred with a mechanical stirrer at 750 rpm in order toflocculate the furnish prior to the drainage tests. Product performancewas tested by adding to a paper furnish 40 lb/t (dry furnish weightbasis) of cationic potato starch (DS=0.03) and 2 lb/t (SiO₂ basis) ofthe product being tested.

Additions to a Britt jar were made 30 seconds apart. Mixing was stopped15 seconds after the addition of the product test samples. Theflocculated furnish was then transferred to a Canadian Standard Freenesstester and drainage measurements were made. Water collected from thefreeness tester was measured for turbidity as an indication of theeffectiveness of the samples to aid retention of the pulp fiber andfiller.

Tests Sample A was prepared by adding 10.0 ml of 5N sulfuric acid to a291-g water solution of sodium silicate containing 2 wt % SiO₂ to lowerthe pH to 9.0. After aging for 5 minutes, aliquots were removed anddiluted to 0.125 wt % SiO₂ for use in the tests.

Test Sample B was prepared utilizing the process of this invention byadding 10.0 ml of 5N sulfuric acid in which 0.68 g of aluminum sulfate[Al₂ (SO₄)₃ •18 H₂ O] had been dissolved to a 291-g water solution ofsodium silicate containing 2 wt % SiO₂ reducing the pH to 8.0. Theresulting polyaluminosilicate had a calculated Al₂ O₃ /SiO₂ molar ratioof 1:100. After aging for 5 minutes aliquots were removed and diluted to0.125 wt % SiO₂ for use in the test; the results are shown in Table 4.

As can be seen from the data, PAS microgels of this invention (Sample B)allowed use of such microgels in paper making under acidic conditionsand reached higher activity as retention/draining agents thanpolysilicate microgels of the prior art (Sample A; U.S. Pat. No.4,954,220) without the addition of aluminum.

                  TABLE 4                                                         ______________________________________                                                     Freeness (ml)/Turbidity                                          Furnish pH     Sample A  Sample B                                             ______________________________________                                        8.0            585/29    650/26                                               7.0            570/32    615/29                                               6.0            535/55    610/25                                               5.0            525/73    610/36                                               4.1            500/82    545/61                                               ______________________________________                                    

We claim:
 1. A process for producing water soluble polyparticulatepolyaluminosilicate microgels having mole ratios of alumina:silica ofbetween 1:25 and 1:1500 comprising the steps of:(a) acidifying anaqueous solution of an alkali metal silicate containing 0.1-6% by weightof SiO₂ to a pH of 2-10.5 by adding an aqueous acidic solutioncontaining sufficient aluminum salt to provide said mole ratios andthereby forming a microgel; and (b) diluting the product of step (a)with water prior to gelation to a SiO₂ content of ≦2% by weight.
 2. Theprocess of claim 1 wherein the mole ratio of alumina:silica is between1:25and 1:1000.
 3. The process of claim 1 wherein the mole ratio ofalumina:silica is between 1:50 and 1:500.
 4. The process of claim 1wherein the acid is a mineral acid containing from 1-50% by weight ofacid.
 5. The process of claim 1 wherein the mole ratio of alumina:silicais between 1:50 and 1:500, the alkali metal silicate is sodium silicate,the acid is a mineral acid and the aluminum salt is aluminum sulfate. 6.The process of claim 1 wherein the mole ratio of alumina:silica isbetween 1:25 and 1:750.
 7. A water soluble polyparticulatepolyaluminosilicate microgel in water consisting essentially of(a)microgels having mole ratios of alumina:silica of between 1:25 and1:1500 wherein aluminum ions are present both intra- and inter-particleand wherein the particles of the microgel have diameter of 1-2 nm; and(b) water such that the microgels are present at ≦2% by weight based onSiO₂ content.